1. Field of the Invention
This invention relates in general to devices to protect building structures from seismic shock, and, in particular, the field of invention relates to devices installed between the frames of structures and vibration-resisting elements provided separately from the frames. The invention also relates to such devices which may be utilized to protect structures from industrially induced vibrations.
2. Description of the Prior Art
When there is a vibration source such as a motor and/or a machine tool in a building, a rubber vibration isolator is generally disposed between the vibration source and the floor to prevent transmission of vibration to the building. However, in the case where the frequency of the vibration source is close to the natural period of the building, the building is liable to resonate. Further, in the case where the vibration source produces rapid vibration, it is difficult for a conventional vibration-isolating mechanism to stop the vibration of the building.
As shown in FIG. 17, when there is a vibration source V such as a motor and/or a machine tool on a certain floor F in the building, a device D may be installed between a beam B and a vibration-resisting element R, capable of resisting the vibration caused by the vibration source V. The device D may be turned on or off as required to thereby control the resonance of the frame relative to the vibration source V. Such a device provides only a limited range of protection to the building frame since it has only two functioning modes, on or off.